Diapoma, Ito & Carvalho & Pavanelli & Vanegas-Ríos & Malabarba, 2022

Ito, Priscila Madoka M., Carvalho, Tiago P., Pavanelli, Carla S., Vanegas-Ríos, James A. & Malabarba, Luiz R., 2022, Phylogenetic relationships and description of two new species of Diapoma (Characidae: Stevardiinae) from the La Plata River basin, Neotropical Ichthyology (e 210115) 20 (1), pp. 1-30 : 19-21

Key to species of Diapoma (Modified from Vanegas-Ríos et al., 2018)

1a. Presence of modified scales on lower caudal-fin lobe, slightly more pronounced in adult males, forming a pocket-shaped structure ........................... 2

1b. Absence of modified scales on lower caudal-fin lobe, caudal scales at base never forming a pocket-shaped structure ................................................... 3

2a. Opercle and subopercle unmodified, not posteriorly prolonged........................... 4

2b. Opercle and subopercle modified, posteriorly prolonged...................................... 5

3a. Complete lateral line ................................................................................................ 6

3b. Incomplete lateral line or discontinuous lateral line............................................... 8

4a. 11–13 gill rakers on lower limb of first gill arch ...................................... D. thauma

4b. 15–18 gill rakers on lower limb of fist gill arch......................................... D. terofali

5a. Snout length 21.3–24.5% HL; maxillary teeth pentacuspid; live specimens with intense red pigmentation on some portions of all fins except pectoral fin .............................................................. D. pyrrhopteryx

5b. Snout length 17.0–21.4% HL; maxillary teeth tricuspid (rarely with more cusps); no red coloration on any fin in live specimens...................................................................................... D. speculiferum

6a. Anal fin unpigmented, without distinctive marks; adipose fin not pigmented in preserved mature males and females; snout to pelvic-fin origin 48.1–52.6% SL ............................................................ D. alburnum

6b. Anal fin pigmented, with distal tip of anterior lobe unpigmented; adipose fin dark in preserved mature males and females; snout to pelvic-fin origin 40.4–46.6% SL ............................................................................. 7

7a. Number of scale rows between dorsal and pelvic-fin origins 11–13 ...... D. itaimbe

7b. Number of scale rows between dorsal and pelvic-fin origins 9–11 ..................... D. dicropotamicus

8a. Body without well-defined, wide lateral band of chromatophores, only narrow lateral stripe present (usually dark)................................... D. pampeana

8b. Body with variedly developed, wide lateral band of intense chromatophores (usually dark or silvery), lateral stripe never reduced to narrow line ............................................................................................ 9

9a. In adult males, anal-fin distal margin strongly convex ........................................ 10

9b. In adult males, anal-fin distal margin somewhat concave, nearly straight or slightly convex .......................................................................... 11

10a. Anal-fin sheath consisting of 20–28 aligned scales, covering three-quarters or entire length of anal-fin base (usually reaching 22nd branched ray); 29–35 branched anal-fin rays (usually 29–33) .......... D. uruguayense

10b. Anal-fin sheath consisting of 23–30 aligned scales reaching no more than half length of anal-fin base (usually extending to 12th or 18th branched ray); 23–30 branched anal-fin rays (usually 25–27) ...................................................................................... D. alegretense

11a. Humeral blotch diffuse or absent; horizontal eye length 31.5–37.0% HL (mean = 35.4% HL)............................................... D. tipiaia

11b. Humeral blotch always discernible; horizontal eye length 36.4–48.5% HL (mean = 41.4% HL)......................................................... 12

12a. Distance between snout to anal-fin origin 52.1–58.8% SL ............... D. lepiclastum

12b. Distance between snout to anal-fin origin 59.3–66.4% SL ................................. 13

13a. First three (often four) dentary teeth tetra or pentacuspid in adults; middle and distal portions of interradial membranes of posterior branched dorsal-fin rays hyaline or, when faintly dusky, being similarly pigmented in both sexes; discontinuous lateral line ............................................ 14

13b. First three (usually four) dentary teeth tricuspid in adults; middle and distal portions of interradial membranes of posterior branched dorsal-fin rays dusky, intensely darker in adult males than in females or juveniles; incomplete lateral line ........................................................................................... 15

14a. Body depth at dorsal-fin origin 27.6–31.9% SL; distance between snout to anal-fin origin 50.8–57.0% SL.......................................... D. potamohadros

14b. Body depth at dorsal-fin origin 35.5–44.1% SL; distance between snout to anal-fin origin 57.1–61.5% SL........................................................... D. obi

15a. Presence of a large dark round blotch on middle region of caudal fin, more noticeable in males; urogenital region darkly pigmented in females; 22–25 gill rakers on first gill arch (mode = 23, 8–9 + 14–17); maximum known body size 30.5 mm SL ................................................. D. guarani

15b. Absence of a large dark blotch on middle region of caudal fin, with caudal spot much more concentrated on peduncle (or partially on interradialis muscles) than on middle caudal-fin rays (rarely faintly scattered dark chromatophores reaching midpoint of ray); urogenital region unpigmented in females; 18–21 gill rakers on first gill arch (mode = 20, 6–8 + 12–14); maximum known body size 59.1 mm SL ...... D. nandi

Phylogenetic analysis. The phylogenetic analysis using molecular data includes 25 species (55 specimens’ samples), of which 15 correspond to Diapoma (37 specimens sampled) (see Tab. S1 ). The concatenated alignment contained 5,039 sites, representing seven markers. The best partition scheme found using PartitionFinder suggests a single partition for 12S and 16S; and 15 partitions representing each codon position of the five genes ( COI, MYH6 , PTR, RAG1, RAG2; Tab. 3 ). The topology using the concatenated dataset is present in Fig. 8 , and the species trees analysis is illustrated in Fig. 9 . For each gene tree representing the seven genes examined with all sequences available in GenBank are available in the Fig. S2 .

The genus Diapoma is recovered as a monophyletic group in both the concatenated analysis (CT) and in the Species Tree (ST) analysis ( PP = 1). The genus is divided into two well supported clades, one composed of ( D. alburnum ( D. dicropotamicus , D. itaimbe )) with high support ( PP =1 CT and ST) which is sister-group to a clade composed of all

other examined species of the genus, including the type species of the genus Cyanocharax ( D. uruguayense ) plus the type species of the genus Diapoma ( D. speculiferum ) ( PP = 0.95 CT and PP = 0.99 for ST). A large monophyletic group, herein named Diapoma uruguayense clade, has a low support ( PP = 0.72 CT; PP = 0.87 ST), being composed of ( D. thauma ( D. alegretense ( D. uruguayense , D. lepiclastum ))) and is sister group to the D. speculiferum clade.

The Diapoma speculiferum clade ( PP = 0.86 CT; PP = 0.73 ST) is composed by eight species and includes the two new species proposed herein. Diapoma potamohadros is closely related to D. tipiaia , with a low support ( PP = 0.62 CT; PP = 0.67 ST), and D. pampeana is highly supported ( PP = 1 CT; PP = 0.97 ST) as the sister-group to the clade ( D. obi and D. guarani ). These two clades formed the sister-group of the well-supported clade ( PP = 0.99 CT; PP = 1 ST) ( D. speculiferum ( D. pyrrhopteryx , D. terofali )).

Figures

FIGURE 2 | Left premaxilla, maxilla and dentary of Diapoma pampeana, UFRGS 8464, 31.9 mm SL, paratype.

FIGURE 8 | Bayesian tree showing the phylogenetic relationships within Diapoma inferred by the concatenated dataset (12S, 16S, COI, MYH6, ptchd1, RAG1, RAG2, total of 5067pb).

FIGURE 9 | Bayesian species tree of Diapoma obtained from multilocus sequences (12S, 16S, COI, MYH6, ptchd1, RAG1, RAG2, total of 5067pb).